What Is Soil?

1. What Is Soil? Image: T. Loynachan Soils-1-1

2. Soil is a layer of unconsolidated material on the Earth’s surface in which plants grow. Image: Louis Maher Image: Professional Soil Classifiers Assoc. of Alabama Soils-1-2

3. Soil is a mixture of mineral grains from the Earth, decomposing organic matter, and voids filled with air or water. Image: Professional Soil Classifiers Assoc. of Alabama Soils-1-3

4. Soil is the Earth material that links living things (biosphere), air (atmosphere), water (hydrosphere), and the solid Earth (geosphere). Image: Bruce Molnia Soils-1-4

5. Why Soils are Important Image: NRCS Soils-5-1

6. Soil is essential for life – even fish depend on nutrients released from soil into streams and oceans. Images: Martin Miller Soils-5-2

7. Soils store water for plants and improve water quality as it passes through them in the hydrologic cycle. Soils-5-3

8. Soils recycle nutrients and carbon. Image: T. Hiett Soils-5-4

9. Soils help recycle people’s waste. Image: T. Hiett Soils-5-5

10. Soils influence how we build our homes, cities, and transportation systems. Image: Digital Stock Soils-5-6

11. Soils Are a Very Important Earth Resource. Image: T. Loynachan Soils-5-7

12. How Soils Form Image: T. Loynachan Soils-2-1

13. Physical weathering breaks rocks into small mineral particles that accumulate on the Earth’s surface. Images: Martin Miller, NRCS Soils-2-2

14. Chemical weathering dissolves and changes minerals that have accumulated on the Earth’s surface. Images: National Cooperative Soil Survey, University of Nebraska Soils-2-3

15. Decomposing organic material from plants and animals mixes with accumulated soil minerals. Images: NRCS, Soil Classifiers of Michigan Soils-2-4

16. Accumulated soil materials contain voids filled with air or water. Image: T. Loynachan Soils-2-5

17. Continued physical and chemical changes over hundreds to thousands of years produce layers called soil horizons. Image: National Cooperative Soil Survey Soils-2-6

18. The Formation of Soils Image: T. Loynachan

19. Soil Dirt is simply misplaced soil!

20. SOIL: A RENEWABLE RESOURCE • Soil is a slowly renewed resource that provides most of the nutrients needed for plant growth and also helps purify water. • Soil formation begins when bedrock is broken down by physical, chemical and biological processes called weathering. • Mature soils have developed over a long time are arranged in a series of horizontal layers,soil horizons.

21. Erosion Transportation Weathering Deposition Igneous rock Granite, pumice, basalt Sedimentary rock Sandstone, limestone Heat, pressure Cooling Heat, pressure, stress Magma (molten rock) Melting Metamorphic rock Slate, marble, gneiss, quartzite Fig. 15-8, p. 343

22. Layers in Mature Soils • Infiltration: the downward movement of water through soil. • Leaching: dissolving of minerals and organic matter in upper layers carrying them to lower layers. • The soil type determines the degree of infiltration and leaching.

23. SOIL: Horizons Figure 3-23

24. Soil Profiles

25. Soil Horizons • O horizon: leaf litter • A horizon: top soil • A horizon comprise the “zone of leaching” • B horizon: subsoil • C horizon: parent material • Bedrock

26. Soil Profiles of the Principal Terrestrial Soil Types Figure 3-24

27. Soil Color Variation

28. Soil Color Variation A horizon: organic coatings B horizon: Iron coatings C horizon: little coating

29. Soil Color Variation

30. Colorful Soils • Red Soil in Southern U.S.

31. Red Sands in Arizona

32. Red Georgia Soil

33. Soil Texture

34. Particle Size Distribution (Texture) • Important for determining suitability for various uses • Considered a basic property because it doesn’t change

35. Properties Related to Texture • Porosity • Permeability • Infiltration • Shrink-swell • Water holding Capacity • Erodibility

36. Soil Separates • Most soils have a combination of soil particles sizes   • Sand • Silt • Clay

37. Soil Particles • Soils vary in the size of the particles they contain, the amount of space between these particles, and how rapidly water flows through them. Figure 3-25

38. Sand • Gritty feel • Can be seen with the naked eye • Hand sampling: • No residue left on hand

39. Silt • Dry: Powdery smooth feel, flour-like • Wet: Creamy slick, slippery feel • No sticky or plastic feel • Can be seen with a hand lens or microscope • Hand sampling: • Coats hand, able to brush off

40. Clay • Dry: Hard feel • Wet: Sticky, plastic feel • Can be seen with an electron microscope • Hand Sampling: • Sticks to fingers

41. Particle Sizes • Clay: less than 0.002 mm • Silt: 0.002-0.05 mm • Sand: 0.05-2 mm • 0.05-0.24 mm fine • 0.25-0.49 mm medium • 0.5-0.99 mm coarse • 1- 2 mm very coarse • Gravels: 2-75 mm • Cobbles:75-250 mm • Stones: 250-600 mm • Boulders: >600 mm

42. Texture by Feel

43. Fine Textured Soil • Large amounts of silt and clay, making it "muddy" when wet  • Pore spaces are small, but numerous and hold more water • As clay soils begin to dry, they may still hold large quantities of water, but adhesive and cohesive properties of water make it unavailable for root uptake

44. Fine Textured Soil

45. Coarse Textured Soil • Large pore spaces and allows water to easily run through it beyond the reach of roots • Drought-prone • Little surface area for the particle volume, reducing fertility

46. Coarse Textured Soil

47. Loamy Soil • A mix of sand, silt, and clay that optimizes agricultural productivity

48. Sand + Silt + Clay = 100% 34 % Sand Texture = CLAY LOAM 33 % Silt 33 % Clay

49. General Influence of Soil Separates on Properties and Behaviors of Soils

50. Soil Texture and Surface Area • As particle size decreases, surface area increases • Clay has about 10,000 times as much surface area as sand • Surface area has a big effect on: • Water holding capacity • Chemical reactions • Soil cohesion • Ability to support microorganisms